1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus and a magnetic recording and reproducing method for causing one or a plurality of write heads to record a plurality of tracks to a piece of magnetic recording media and one or a plurality of read heads to reproduce signals from these tracks.
2. Description of the Related Art
In recent years, efforts have been made to bring about higher recording densities to achieve greater capacities of magnetic recording media using magnetic heads suitable for narrowing the widths of tracks on pieces of the media. Generally, the key to the successful narrowing of tracks is how to improve the accuracy of the tracking servo in use.
As the widths of tracks have been narrowed, it has become increasingly difficult for the servo facility of magnetic tape recording and reproducing apparatuses to progress in accuracy. One proposed solution to that difficulty is the so-called non-tracking system that is now in actual use (e.g., see Japanese Patents Nos. 1842057, 1842058, and 1842059; and Japanese Patents Laid-open Nos. Hei 04-370580 and Hei 05-020788). The non-tracking system involves having data recorded in blocks for identification purposes to tracks that are recorded by helical scan with a double azimuth head arrangement. Even if data is not reproduced from the target track by a single trace, the system allows the data to be reconstituted later. The non-tracking system provides at least four times as much margin for tracking control within a single track as traditional tracking servo systems require.
The non-tracking technique has been considered for possible use in linear recording in addition to helical scan (e.g., see Japanese Patents Laid-open Nos. Hei 10-283620 and 2003-132504).
Where the substrate for magnetic recording media is an elastic nonmagnetic support such as polyester film, the allowable amount of deformation in the substrate is typically up to about twice the track width applicable to double azimuth recording in combination with a tracking servo. A larger amount of deformation than that would make it impossible to reproduce signals with a high enough S/N ratio from the media. For recording without recourse to the double azimuth feature, each of so-called guard bands separating tracks is required in size to be no greater than the amount of deformation in the tape in combined use with the tracking servo. The requirement needs to be met to prevent degradation of reliability in such factors as error rate.
The problem above is attributable to the fact that typical signal reproduction systems so far have left their signal quality to deteriorate considerably while using at least one read head to read signals concurrently from a plurality of tracks. The bottleneck has been bypassed traditionally by providing guard bands in conjunction with the double azimuth arrangement and by getting the read head to read signals from one track only.
However, provision of guard bands is an impediment to higher track densities. Moreover, double azimuth recording, which is supposed to minimize interference between adjacent tracks during reproduction, tends to lose its effectiveness when the tracks are arranged to be narrowed.
The same applies to the non-tracking system as well. That is, although signals are apparently reproduced by the read head concurrently from a plurality of tracks, the read head in fact reproduces the data always from a single track from a time-shared point of view. Signals are never reproduced simultaneously from a plurality of tracks.
Where non-tracking systems are designed to address ever-higher track densities, they tend to suffer from noise stemming from signals picked up from tracks adjacent to the target track. Apparently, there exists a limit to how much narrower the tracks can be arranged to be.
In a proposed technique belonging to the related art of magnetic head devices, a plurality of magnetic recording layers or magnetic read head layers each having the same magnetic head element are stacked on the substrate composed of a nonmagnetic material. All magnetic head elements are then shifted in a direction substantially perpendicular to the stacking direction (the perpendicular direction is called the head width direction). This arrangement is disclosed illustratively in Japanese Patents Laid-open Nos. 2002-216313 and 2002-157710.
In another development aimed at boosting recording density, there is proposed a technique for recording a plurality of data frames concurrently using a plurality of heads forming a single block of the same azimuth (e.g., see Japanese Patents Laid-open Nos. 2003-338012 and 2004-071014).
The proposed techniques outlined above involve narrowing the read head width to about half the track width. This constitutes restrictions on attempts to increase the output of reproduction signals. Illustratively, a sufficiently high S/N ratio is difficult to sustain with these techniques. Overall, these techniques are not necessarily suitable for attaining ever-higher recording densities.
Meanwhile, MIMO (multi-input/multi-output) technology is a well-known technology for use in wireless communications (e.g., see Japanese Patent No. 3664993).
Also known are techniques for applying MIMO technology to magnetic recording (e.g., see IEEE Paper Trans. Mag. Vol. 30, No. 6; November 1994, page 5100). However, there are problems yet to be cleared before commercialization, including how to employ a read head wider than a recorded track.
The present invention proposes techniques which are designed to apply MIMO technology to magnetic recording and which were not anticipated from the related art including the above-cited paper.